Motorola Corporation

Michelle M Bray

Michael W Bright

Alan L Wilson

Hans Christopher Sowa

Eric F Ziolko

David L Weiss

Harry A Hennen

Mark J Sherly

A key management system permits a high degree of autonomous rekeying activity by communication units (105) in a secure communication system (100). Responsive to time reference information transmitted by a key management controller (101), the communication units (105) activate a designated key index at a predetermined activation time. If conditions so indicate, a communication unit may transmit a rekey request.

Encryption key management

A single sync field (501) and multiple messages or message segments (503, 507, 511, and 515) are chained (407) together and encrypted (407) as a whole. When this encrypted chained message is received, it is decrypted as a whole (605), or in part (613) by setting up (609) and filling (611) a holding register with the encryption state of the encrypting device.

Encryption and decryption of chained messages

Disclosed is a method and apparatus for time companding a digital voice signal wherein, single bits are periodically removed from the digital voice signal, which is then compressed thereby forming a contiguous area of removed bits. A synchronization signal is inserted into this area and the combined signal is transmitted. At the receiver, the synchronization signal is extracted and is used to synchronize the receiver. The digital voice signal is then expanded and the removed bits are predicted and replaced.

Method and apparatus for time companding a digital voice signal

Disclosed is a synchronous secure communication system wherein an information signal is encrypted in an encryption means. The encrypted signal is compressed to allow the insertion of a synchronization signal, and the combined signals are transmitted. At the receiver, the synchronization signal is extracted and used to synchronize the receiver to the incoming data stream thereby improving receiver sensitivity and range.

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Schaumburg, IL, United States of America

Michelle M Bray